Develop Reference

ResultSet not open although i have only one at a time

I know many questions were asked before for this issue but for this situations I can't find an answer.
This is my code:
private Collection<Coupon> getCouponsMain(Company company, String filters) throws DAOException
{
String sql = null;
if (filters != null)
{
sql = "SELECT couponsystem.coupon.* FROM couponsystem.company_coupon LEFT JOIN couponsystem.coupon ON "
+ "couponsystem.company_coupon.COUPON_ID = couponsystem.coupon.ID WHERE couponsystem.company_coupon.COMP_ID = ? AND ?";
}
else
{
sql = "SELECT couponsystem.coupon.* FROM couponsystem.company_coupon LEFT JOIN couponsystem.coupon ON "
+ "couponsystem.company_coupon.COUPON_ID = couponsystem.coupon.ID WHERE couponsystem.company_coupon.COMP_ID = ?";
}
try (Connection con = pool.OpenConnection(); PreparedStatement preparedStatement = con.prepareStatement(sql);)
{
// query command
preparedStatement.setLong(1, company.getId());
if (filters != null)
{
preparedStatement.setString(2, filters);
}
ResultSet rs = preparedStatement.executeQuery();
if (rs.next())
{
CouponDBDAO couponDao = new CouponDBDAO();
rs.previous();
return couponDao.BuildCoupons(rs);
}
else
{
return null;
}
}
catch (SQLException | NullPointerException e)
{
throw new DAOException("Failed to retrieve data for all coupons" + e.getMessage());
}
}
I think the query itself is not the important issue here but, once I use next() for the ResultSet, I get the error:
java.sql.SQLException: Operation not allowed after ResultSet closed"
This usually happened when using two rs for same statement, this is not the case this time.
Due to many issues with previous method and BuildCoupons(rs) issue, also this part does not work properly for the same reason:
#Override
public Company getCompany(long id) throws DAOException
{
String sql = "SELECT * FROM couponsystem.company WHERE ID = ?";
try (Connection con = pool.OpenConnection(); PreparedStatement preparedStatement = con.prepareStatement(sql);)
{
// query command
preparedStatement.setLong(1, id);
// query execution
ResultSet rs = preparedStatement.executeQuery();
Company comp = new Company();
if (rs.next())
{
//Fill customer object from Customer table
comp.setId(rs.getLong("ID"));
comp.setCompName(rs.getString("COMP_NAME"));
comp.setPassword(rs.getString("PASSWORD"));
comp.setEmail(rs.getString("EMAIL"));
comp.setCoupons(comp.getCoupons());
}
else
{
comp = null;
}
return comp;
}
catch (SQLException e)
{
throw new DAOException("Failed to retrieve data for customer id: " + id);
}
}
BTW - working with MySQL and insert, update and delete queries are working properly so there not issue with the connection to the db
Another update -
Once i replace it to regular statement, it's working but of course i'm losing all the advantages of prepared statement
Like i said i create new code in order to isolate the big program
This is the code:
public class testState
{
public static void main(String[] args) throws SQLException
{
DBDAO pool = DBDAO.getInstance();
String sql = "SELECT ID FROM couponsystem.company WHERE COMP_NAME = ? AND PASSWORD = ?";
String compName = "t";
String password = "t";
pool.CreatePool();
Connection con = pool.OpenConnection();
PreparedStatement preparedStatement = con.prepareStatement(sql);
preparedStatement.setString(1, compName);
preparedStatement.setString(2, password);
preparedStatement.executeQuery();
ResultSet rs = preparedStatement.executeQuery();
System.out.println("rs status: " + rs.isClosed());
if (rs.next())
{
System.out.println("log-in was successfuly performed");
System.out.println(rs.getLong(1));
System.out.println("hjhjh");
}
else
{
System.out.println("-1");
}
rs.close();
preparedStatement.close();
con.close();
pool.CloseConnection();
}
}

Problem was solved,
this is the problem:
sql = "SELECT couponsystem.coupon.* FROM couponsystem.company_coupon LEFT JOIN couponsystem.coupon ON "
+ "couponsystem.company_coupon.COUPON_ID = couponsystem.coupon.ID WHERE couponsystem.company_coupon.COMP_ID = ? AND ?";
the second ? is illegal, but the exception is ResultSet closed and not query issue

the problem is you are trying to go back to the previous record in the result set which is not possible.
learn about scrollable resultset and make it insensitive, once you use this you can go back to the previous record by using rs.previous()
ResultSet.TYPE_SCROLL_INSENSITIVE

Java JDBC query not accepted

Hey I'm making a little webapp and have a java file in it with a function what connects a db and fetches the data.
But I'm getting a exception anyone knows why because my query is valid if I'm right.
I use eclipse and mysql workbench.
Function:
import java.sql.*;
public class Functions {
public void dbConn(String nVal, String inpVal){
System.out.println("Running function...");
if(nVal != null || inpVal != null){
String sqlSerch;
if(nVal.equals("name")){
sqlSerch = "ID, aNaam FROM profiles WHERE naam = 'casper'";
}else{
sqlSerch = "naam, aNaam FROM profiles WHERE ID = " + inpVal;
}
//driver / db path
final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
final String DB_URL = "jdbc:mysql://localhost:3306/profile";
//DB user&password
final String USER = "root";
final String PASS = "";
//declare con & sql var
Connection conn = null;
Statement stmt = null;
//register jdbc driver
try{
Class.forName(JDBC_DRIVER);
//make a connection
conn = DriverManager.getConnection(DB_URL,USER,PASS);
//SQL Statement
stmt = conn.createStatement();
String sql = "SELECT "+ sqlSerch;
ResultSet rs = stmt.executeQuery(sql);
//Declareer variablen met data uit db
//int id = rs.getInt("ID");
String naam = rs.getString("naam");
String aNaam = rs.getString("aNaam");
System.out.println( naam + aNaam);
rs.close();
stmt.close();
conn.close();
}catch(Exception e){
System.out.println(e);
}
System.out.println(" - " + nVal + " - " + inpVal);
}
}
}
exception:
java.sql.SQLException: Column 'naam' not found.
database structure:
Thank you in advance,
Casper

When you receive "name" through the nVal parameter, you select only ID and aNaam columns.
So, if you try to get values for naam from that ResultSet you get the Exception.
Also, I suggest limiting the results of your query to 1, since you use the WHERE clause with naam and ID, which seem to be not unique, unless there's some constraint not included in the screenshot.
Hope this helped.

You branch and create your queries:
if(nVal.equals("name")){
sqlSerch = "ID, aNaam FROM profiles WHERE naam = 'casper'";
}else{
sqlSerch = "naam, aNaam FROM profiles WHERE ID = " + inpVal;
}
Then regardless of the branch, you get your result set values:
String naam = rs.getString("naam");
String aNaam = rs.getString("aNaam");
But "naam" will not be in your "ID, aNaam" search.
In general, a good rule of thumb is to always return the same columns.

Getting SQL exception in where clause while inserting data in database through java

I want to store the password for required ID using java. Everything is working fine except that I am getting this Exception
"SQL Exception thrown: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '(Pass_word) set Pass_word = 'pass' where ID = 2' at line 1".
I am getting this exception only in update query but not in select query.I am using Eclipse. Can anyone tell me what I am doing is wrong?
import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Scanner;
public class information {
public static void main(String[] args) {
String password;
ResultSet rs;
String queryString;
int x=1;
try
{
Class.forName("com.mysql.jdbc.Driver");
Connection conn = null;
conn = DriverManager.getConnection("jdbc:mysql://localhost/onlineexam","root", "batch12#nitap");
System.out.print("Database is connected !");
Statement stmt = conn.createStatement();
PreparedStatement pstmt = null;
while(x==1)
{
System.out.println("Press 1 to enter student id");
System.out.println("Press 2 to exit");
Scanner s= new Scanner(System.in);
int choice = s.nextInt();
switch(choice)
{
case 1: System.out.println("Enter the ID of student");
int id = s.nextInt();
queryString = "select ID,Roll_no, Course_name, Course_code, Date,Time from student_reg where ID=" +id;
rs= stmt.executeQuery(queryString);
//System.out.println(rs.getInt("ID"));
while(rs.next())
{
if(rs.getInt("ID")== id)
{
String roll = rs.getString("Roll_no");
String date = rs.getString("Date");
String time = rs.getString("Time");
String c_name = rs.getString("Course_name");
String c_code = rs.getString("Course_code");
password pass1= new password(roll,date,time,c_name,c_code);
pass= pass1.passwd();
System.out.println(pass);
queryString =" Update student_reg(Pass_word) set Pass_word = 'pass' where ID = ?";
//queryString= "INSERT INTO student_reg(Password) VALUES ('password') where ID = ?";
//stmt.executeUpdate(queryString);
//PreparedStatemenet pstmt = conn.preparedStatement("INSERT INTO student_reg(Password) VALUES ('password') where ID = ?");
//pstmt.setLong(1, id);
pstmt = conn.prepareStatement(queryString);
pstmt.setInt(1, id);
int numberOfUpdatedRecords = pstmt.executeUpdate();
s.close();
}
}
break;
case 2: x=0;
}
}
if(conn!= null)
{
stmt.close();
pstmt.close();
conn.close();
conn = null;
}
}
catch(ClassNotFoundException cnf)
{
System.out.println("Driver could not be loaded: " + cnf);
}
catch(SQLException sqle)
{
System.out.println("SQL Exception thrown: " + sqle);
}
catch(Exception e)
{
System.out.print("Do not connect to DB - Error:"+e);
}
}
}

Your code has many problem:
queryString = "select ID,Roll_no, Course_name, Course_code, Date,Time from student_reg where ID= id";
This line you have condition where but you not set the value yet, you should set
queryString = "select ID,Roll_no, Course_name, Course_code, Date,Time from student_reg where ID = " + id;
Better if you take a look at PreparedStatement for prevent SQL Injection as well.
The last one:
queryString= "INSERT INTO student_reg(Password) VALUES ('password') where ID = id";
This line seem you want to update something. Please review it.

queryString = "select ID,Roll_no, Course_name, Course_code, Date,Time from student_reg where ID= id";
should be
queryString = "select ID,Roll_no, Course_name, Course_code, Date,Time from student_reg where ID = " + id;
This would fix the error, but it would be better to use a PreparedStatement, where the query String looks like "select ID,Roll_no, Course_name, Course_code, Date,Time from student_reg where ID = ?", and you pass the id as a parameter.

It is so obvious because you shouldn't include the 'id' in your query string:
queryString = "select ID,Roll_no, Course_name, Course_code, Date,Time from student_reg where ID = " + id;
Very good hint from #spencer: you can not use WHERE clause in your INSERT INTO statement. Probably you wanted to UPDATE a row with that id. Also it is better to do it using PreparedStatemenet to avoid such mistakes:
conn = DriverManager.getConnection("jdbc:mysql://localhost/onlineexam","root", "batch12#nitap");
PreparedStatemenet pstmt = conn.preparedStatement("UPDATE student_reg SET password = 'password' where ID = ?");
pstmt.setLong(1, id);
int numberOfUpdatedRecords = pstmt.executeUpdate();
I suggest you to rename the column name password, because it is a reserved word in mysql, so you may get strange results working with that column name. Change it to some other thing like: pass_word or passwd , ... . As you may know you can use keywords as column names in your queries using some quotes or other things but it is more safe to rename it to another name, just for hint.
if you use this connection without a connection-pool, you may want to close the Statement and the Connection.
Good Luck.

How to use two excel sheet to read data in java using JDBC-ODBC?

I want to read the data from two excel sheets using JDBC. So i have setup two data sources(system DSN names) for both excel sheets.Now i'm able to read the data from one excel sheet ? But how to connect the second the excel sheet ?
Please see the below coding to read the data from one excel sheet.But how to use second data source name in the second connection ? Can you please advise.
public class MergeXSLFiles {
public static Connection getConnection() throws Exception {
String driver = "sun.jdbc.odbc.JdbcOdbcDriver";
String url = "jdbc:odbc:Report";
String username = "";
String password = "";
Class.forName(driver);
return DriverManager.getConnection(url, username, password);
}
public static void main(String args[]) throws Exception {
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
conn = getConnection();
stmt = conn.createStatement();
String excelQuery = "select * from [Sheet$]";
rs = stmt.executeQuery(excelQuery);
while (rs.next()) {
System.out.println(rs.getString("name") + " " + rs.getString("age"));
}
rs.close();
stmt.close();
conn.close();
}
}
Thanks for help.

String excelQuery = "select * from [Sheet$]1";
String excelQuery2 = "select * from [Sheet$]2";
rs = stmt.executeQuery(excelQuery);
while (rs.next()) {
System.out.println(rs.getString("name") + " " + rs.getString("age"));
}
rs = stmt.executeQuery(excelQuery2);
while (rs.next()) {
System.out.println(rs.getString("name") + " " + rs.getString("age"));
}
Just execute the other query to get the results from the next sheet

MySQL exception - com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException

I get the error:
'Unknown column 'customerno' in 'field list' '.
But, that column exists in my customer table. Then why am I getting this exception ?
Code:
import java.sql.*;
public class Classy {
static String myQuery =
"SELECT customerno, name" +
"FROM customers;";
public static void main(String[]args)
{
String username = "cowboy";
String password = "1234567";
try
{
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/Business", username, password);
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(myQuery);
while(rs.next())
{
System.out.print(rs.getString("customerno"));
}
} catch(SQLException ex){System.out.println(ex);}
}
}

Look at what your query really is. This:
static String myQuery =
"SELECT customerno, name" +
"FROM customers;";
is equivalent to:
static String myQuery = "SELECT customerno, nameFROM customers;";
Now can you see what's wrong? I'm surprised it complained about customerno rather than the lack of a FROM part...
Note that I suspect you don't want the ; either. I'd write it all one one line just for readability, when you can, as well as limiting the accessibility and making it final:
private static final String QUERY = "SELECT customerno, name FROM customers";

the problem with your syntax is that you have no space between name and FROM
String myQuery =
"SELECT customerno, name" + // problem is here
"FROM customers;";
instead add a space after name
String myQuery =
"SELECT customerno, name " + // add space here
"FROM customers";

import java.sql.*;
public class Classy {
static String myQuery =
"SELECT customerno, name" +
"FROM customers;";
public static void main(String[]args)
{
String username = "cowboy";
String password = "1234567";
try
{
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/Business", username, password);
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(myQuery);
while(rs.next())
{
//Try and change this with the numeric value that is present in the database,
e.g if it's column 2 do something like
rs.getString(1);
System.out.print(rs.getString("customerno"));
}
}catch(SQLException ex){System.out.println(ex);}
}
}